Add Qualcomm QDB (Qshrink Database) format

This is a very simple wrapper around compressed XML used by Qualcomm to
store modem debug info. I gather that these files are used by Qualcomm's
official QXDM diagnostic software, but I derived the format without
reference to any documentation or tooling; it's just that simple.

firmware/qualcomm_qdb.ksy

@@ -0,0 +1,25 @@
+meta:
+  id: qualcomm_qdb
+  title: Qualcomm Qshrink hash database file
+  application: Qualcomm QXDM
+  file-extension: qdb
+  license: CC0-1.0
+
+doc: |
+  This format is nothing more than zlib-compressed XML appended to a trivially
+  simple binary header. The XML maps diagnostic codes emitted by Qualcomm modem
+  firmware to textual log messages. A file of this type typically resides on the
+  "modem" partition of a Qualcomm device with a name like "qdsp6m.qdb".
+
+seq:
+  - id: magic
+    contents: [0x7f, "QDB"]
+  - id: guid
+    size: 0x10
+    doc: Matches the top-level <GUID> element in the compressed XML
+
+instances:
+  compressed_xml:
+    pos: 0x40
+    size-eos: true
+    process: zlib